1. Field of the Invention
The present invention relates to a sound signal playback machine and method thereof for playing back multichannel sounds.
2. Description of the Related Art
Concerning the sound signal playback machine for playing back multichannel sounds, for example, a sound signal playback machine to realize 5.1 surround playback is well known. FIG. 10 is a block diagram showing an example of such a sound signal playback machine. In FIG. 10, the signal input terminal 101, to which sound signal SL of L-channel (left channel) is supplied, is connected to the speaker 131, which is arranged at the front on the left, via HPF (high-pass filter) 111 and the amplifier 121. At the same time, the signal input terminal 101 is connected to the signal adder 151 via LPF (low-pass filter) 141. The signal input terminal 102, to which sound signal SR of R-channel (right channel) is supplied, is connected to the speaker 132, which is arranged at the front on the right, via HPF 112 and the amplifier 122. At the same time, the signal input terminal 102 is connected to the signal adder 151 via LPF 142. The signal input terminal 103, to which sound signal SSL of SL-channel (surround left channel) is supplied, is connected to the speaker 133, which is arranged at the rear on the left, via HPF 113 and the amplifier 123. At the same time, the signal input terminal 103 is connected to the signal adder 151 via LPF 143. The signal input terminal 104, to which sound signal SSR of SR-channel (surround right channel) is supplied, is connected to the speaker 134, which is arranged at the rear on the right, via HPF 114 and the amplifier 124. At the same time, the signal input terminal 104 is connected to the signal adder 151 via LPF 144. Further, the signal input terminal 105, to which sound signal SC of C channel (central channel) is supplied, is connected to the speaker 135, which is arranged at the front center, via HPF 115 and the amplifier 125. At the same time, the signal input terminal 105 is connected to the signal adder 151 via LPF 145. On the other hand, the signal input terminal 106, to which sound signal SLFE of LFE channel (channel exclusively used for the low frequency band) is supplied, is connected to the signal adder 152 to which the above signal adder 151 is connected. This signal adder 152 is connected to the speaker 136, which is arranged on the side, via the amplifier 126. In this case, the speakers 131 to 135 respectively compose a speaker system for playing back sounds of middle low frequency and higher frequency than that. In general, they are referred to as a satellite speaker system. The speaker 136 is a speaker system for playing back sounds of low frequency. In general, the speaker 136 is referred to as a sub-woofer.
In this connection, the above conventional sound signal playback machine is designed so that the frequency response can be flat when signals on the low frequency side and those on the high frequency side are electrically synthesized with each other. Further, in the above conventional sound signal playback machine, it is necessary to use a filter of the high order so that the band width, in which the frequency response on the low frequency side and that on the high frequency side cross each other, can be reduced. Accordingly, the following problems may be encountered. The frequency response of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, are flat as shown in FIG. 11, however, as shown in FIG. 12, a group delay in the low frequency band is increased, which causes such a problem that sounds of low frequency can not be faithfully played back and further a nuance of sounds of a musical instrument of low frequency is changed. In the case where sound signal SLFE of channel LFE and sound signals SL to SC of the other channels (main channels) are correlated with each other, a group delay is increased in the low frequency band when sound signal SLFE in channel LFE is added.
The present invention has been accomplished in view of the above circumstances. It is an object of the present invention to provide a sound signal playback machine and method thereof capable of making a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are synthesized with each other, flat so that sounds of low frequency can be faithfully played back and a nuance of sounds of a musical instrument of low frequency can be improved.
In order to accomplish the above object, first, the present invention provides a sound signal playback machine comprising: a high frequency pass filter for extracting a predetermined high frequency component from a sound signal in a main channel; a first speaker for playing back the high frequency component extracted by the high frequency pass filter; a low frequency pass filter for extracting a predetermined low frequency component from the sound signal in the main channel; a signal adder for outputting an addition signal in which the low frequency component extracted by the low frequency pass filter is added to a sound signal in a channel exclusively used for a low frequency band; and a second speaker for playing back the addition signal outputted from the signal adder, wherein the degree of the low frequency pass filter is set higher than that of the high frequency pass filter, the sound signal playback machine further comprising a phase matching means for matching the phase of the high frequency component extracted by the high frequency pass filter with the phase of the low frequency component extracted by the low frequency pass filter. According to the sound signal playback machine composed as described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Secondly, the present invention provides a sound signal playback machine according to the above item 1, wherein the phase matching means is a delay circuit for delaying the high frequency component extracted by the high frequency pass filter. According to the sound signal playback machine composed as described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Thirdly, the present invention provides a sound signal playback machine according to the above item 2, wherein delay time T1 (sec) of the delay circuit is set at a value calculated by the equation of
T1=(xcfx861xe2x88x92xcfx862+xcfx80xc2x7n)/(2xcfx80Fc) 
(n=. . . xe2x88x922, xe2x88x921, 0, 1, 2 . . . )
where xcfx861 (rad) is a phase angle at a cut-off frequency Fc (Hz) of the high frequency pass filter, and xcfx862 (rad) is a phase angle of the low frequency pass filter. According to the sound signal playback machine composed as described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Fourthly, the present invention provides a sound signal playback machine according to the above item 1, wherein the phase matching means is to set the first speaker by moving it in a direction so that the first speaker can be separated from a listener. According to the sound signal playback machine composed as described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Fifthly, the present invention provides a sound signal playback machine according to the above item 1, wherein the phase matching means is to set the second speaker by moving it in a direction so that the second speaker can be approached to a listener, and the phase matching means is also a delay circuit for delaying the addition signal outputted from the signal adder. According to the sound signal playback machine composed as described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Sixthly, the present invention provides a sound signal playback machine according to one of the above items 1 to 5, further comprising an auxiliary phase matching means for matching the phase of the low frequency component extracted by the low frequency pass filter with the phase of the sound signal in the channel exclusively used for the low frequency band. According to the sound signal playback machine composed as described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat. Even when sound signals in the channel exclusively used for the low frequency band and sound signals in the main channel are correlated with each other, there is no possibility that the group delay is increased in the low frequency band.
Seventhly, the present invention provides a sound signal playback machine according to the above item 6, wherein the auxiliary phase matching means is a delay circuit for delaying the sound signal in the channel exclusively used for the low frequency band. According to the sound signal playback machine composed as described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat. Even when sound signals in the channel exclusively used for the low frequency band and sound signals in the main channel are correlated with each other, there is no possibility that the group delay is increased in the low frequency band.
Eighthly, the present invention provides a sound signal playback machine according to the above item 7, wherein delay time T2 (sec) of the delay circuit is set at a value calculated by the equation of
T2=(xcfx861+xcfx80xc2x7n)/(2xcfx80xc2x7Fc) 
(n=. . . xe2x88x922, xe2x88x921, 0, 1, 2 . . . )
where xcfx861 (rad) is a phase angle at a cut-off frequency Fc (Hz) of the high frequency pass filter. According to the sound signal playback machine composed as described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat. Even when sound signals in the channel exclusively used for the low frequency band and sound signals in the main channel are correlated with each other, there is no possibility that the group delay is increased in the low frequency band.
Ninthly, the present invention provides a sound signal playback machine according to one of the above items 1 to 5, further comprising a phase inversion circuit for inverting a phase of the low frequency component extracted by the low frequency pass filter when a difference between the phase of the low frequency component extracted by the low frequency pass filter and the phase of the sound signal in the channel exclusively used for the low frequency is xcfx80 (rad). According to the sound signal playback machine composed as described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Tenthly, the present invention provides a sound signal playback method comprising the steps of: extracting a predetermined high frequency component from a sound signal in a main channel by a high frequency pass filter; playing back the high frequency component, which has been extracted by the high frequency pass filter, by a first speaker; extracting a predetermined low frequency component from the sound signal in the main channel by a low frequency pass filter; adding the low frequency component extracted by the low frequency pass filter to a sound signal in the channel exclusively used for the low frequency by a signal adder and outputting an addition signal; and playing back the addition signal, which has been outputted from the signal adder, by a second speaker, wherein the degree of the low frequency pass filter is set higher than that of the high frequency pass filter, and the phase of the high frequency component extracted by the high frequency pass filter and the phase of the low frequency component extracted by the low frequency pass filter are matched with each other. According to the sound signal playback method described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Eleventhly, the present invention provides a sound signal playback method according to the above item 10, wherein the phase of the high frequency component extracted by the high frequency pass filter and the phase of the low frequency component extracted by the low frequency pass filter are matched with each other when the high frequency component extracted by high frequency pass filter is delayed by the delay circuit. According to the sound signal playback method described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Twelfthly, the present invention provides a sound signal playback method according to the above item 11, wherein delay time T1 (sec) of the delay circuit is set at a value calculated by the equation of
T1=(xcfx861xe2x88x92xcfx862+xcfx80xc2x7n)/(2xcfx80xc2x7Fc) 
(n=. . . xe2x88x922, xe2x88x921, 0, 1, 2 . . . )
where xcfx861 (rad) is a phase angle at a cut-off frequency Fc (Hz) of the high frequency pass filter, and xcfx862 (rad) is a phase angle of the low frequency pass filter. According to the sound signal playback method described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Thirteenthly, the present invention provides a sound signal playback method according to the above item 10, wherein the phase of the high frequency component extracted by the high frequency pass filter and the phase of the low frequency component extracted by the low frequency pass filter are matched with each other when the first speaker is arranged by moving so that it can be separated from a listener. According to the sound signal playback method described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Fourteenthly, the present invention provides a sound signal playback method according to the above item 10, wherein the phase of the high frequency component extracted by the high frequency pass filter and the phase of the low frequency component extracted by the low frequency pass filter are matched with each other when the second speaker is arranged by moving so that it can be separated from a listener and the addition signal outputted from the signal adder is delayed by the delay circuit. According to the sound signal playback method described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.
Fifteenthly, the present invention provides a sound signal playback method according to one of the above items 10 to 14, wherein the phase of the low frequency component extracted by the low frequency pass filter and the phase of the sound signal in the channel exclusively used for the low frequency band are matched with each other. According to the sound signal playback method described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat. Even when sound signals in the channel exclusively used for the low frequency band and sound signals in the main channel are correlated with each other, there is no possibility that the group delay is increased in the low frequency band.
Sixteenthly, the present invention provides a sound signal playback method according to the above item 15, wherein the phase of the low frequency component extracted by the low frequency pass filter and the phase of the sound signal in the channel exclusively used for the low frequency band are matched with each other by delaying the sound signal in the channel exclusively used for the low frequency band by the delay circuit. According to the sound signal playback method described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat. Even when sound signals in the channel exclusively used for the low frequency band and sound signals in the main channel are correlated with each other, there is no possibility that the group delay is increased in the low frequency band.
Seventeenthly, the present invention provides a sound signal playback method according to the above item 16, wherein delay time T2 (sec) of the delay circuit is set at a value calculated by the equation of
T2=(xcfx861+xcfx80xc2x7n)/(2xcfx80xc2x7Fc) 
(n=. . . xe2x88x922, xe2x88x921, 0, 1, 2 . . . )
where xcfx861 (rad) is a phase angle at a cut-off frequency Fc (Hz) of the high frequency pass filter. According to the sound signal playback method described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat. Even when sound signals in the channel exclusively used for the low frequency band and sound signals in the main channel are correlated with each other, there is no possibility that the group delay is increased in the low frequency band.
Eighteenthly, the present invention provides a sound signal playback method according to one of the above items 10 to 14, wherein the phase of the low frequency component extracted by the low frequency pass filter is inverted by the phase inversion circuit when a difference between the phase of the low frequency component extracted by the low frequency pass filter and the phase of the sound signal in the channel exclusively used for the low frequency is xcfx80 (rad). According to the sound signal playback method described above, it is possible to make a group delay characteristic of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, substantially flat.